Polarization Multiplexed Transceiver Pilot Tone Segmentation

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Solution Overview

Problem

Current optical transceivers face challenges in scalability, power consumption, spectral efficiency, and noise tolerance, particularly with high-order modulation constellations and tight channel spacing, leading to reduced reach and increased complexity in digital signal processing.

Innovation Solution

The implementation of a polarization multiplexed optical transceiver using pilot tones and a combination of analog and digital signal processing for self-demultiplexed detection, which simplifies digital signal processing algorithms and reduces power consumption while maintaining spectral efficiency and tolerance to chromatic dispersion, polarization mode dispersion, and amplified spontaneous emission noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If high-order modulation constellations (e.g., 16-QAM) are used to increase information transmission capacity, then capacity increases, but noise susceptibility increases and optical unregenerated reach decreases

Engineering Contradiction:

Improveinformation transmission capacityVSAvoidnoise susceptibility and optical reach

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent segments the high-order modulation signal into multiple lower-rate subcarriers using OFDM. Instead of transmitting one high-capacity signal that is highly susceptible to noise, the system divides it into multiple parallel lower-capacity subcarriers that can be transmitted more reliably and then recombined at the receiver, thus maintaining capacity while improving noise tolerance

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements adaptive modulation where the modulation constellation size (M in M-QAM) can be dynamically adjusted based on channel conditions. When noise levels are high, the system automatically reduces to lower-order modulation (e.g., QPSK) to maintain reliable transmission, and when conditions are good, it increases to higher-order modulation to maximize capacity

Inventive Principle:

Principle #15Dynamics

2Productivity

If tight channel spacing is used to improve spectral efficiency, then spectral efficiency increases, but channel separation becomes more difficult and interference increases

Engineering Contradiction:

Improvespectral efficiencyVSAvoidchannel separation complexity and interference management

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent uses OFDM to segment the available spectrum into multiple orthogonal subcarriers with precise frequency spacing. Each subcarrier is separated in the frequency domain by the FFT process at the receiver, allowing tight spectral packing while maintaining clean channel separation through the mathematical orthogonality of the subcarriers

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces cyclic prefix as an intermediary time-domain extension between OFDM symbols. This cyclic prefix acts as a guard interval that prevents inter-symbol interference and inter-carrier interference, enabling tight frequency spacing while maintaining signal integrity through the intermediary protective structure

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If digital signal processing algorithms are used to compensate for channel impairments, then signal quality improves, but power consumption increases

Engineering Contradiction:

Improvesignal quality and impairment compensationVSAvoidDSP power consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent replaces complex iterative digital signal processing with simpler analog/RF domain processing for functions like frequency offset correction and phase synchronization. By using analog techniques (e.g., phase-locked loops, frequency mixing) instead of computationally intensive digital algorithms, the system achieves similar impairment compensation with significantly reduced power consumption

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Productivity

If polarization multiplexing is used to double transmission capacity, then capacity increases, but polarization demultiplexing becomes complex and sensitive to polarization mode dispersion

Engineering Contradiction:

Improvetransmission capacityVSAvoidpolarization demultiplexing complexity and PMD sensitivity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent segments the polarization multiplexed signal into orthogonal polarization components and further segments each into OFDM subcarriers. The FFT process naturally separates the orthogonal polarizations into distinct signal streams that can be independently processed, simplifying the demultiplexing operation and reducing sensitivity to polarization mode dispersion effects

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS8699880B2Optical transceivers for use in fiber optic communication networks

Publication Date: 2014.04.15 CIENA CORP

AI summary

The present disclosure provides a polarization multiplexed transceiver, including: a transmitter; a receiver; circuitry within the transmitter configured to insert pilot tones as a reference state of polarization for a polarization multiplexed signal; and circuitry within the receiver configured to de-multiplex the polarization multiplexed signal using the pilot tones. The transmitted signal is constructed in such a manner as to facilitate the division of the receiver processing between the analog and digital domains such that the implementation may be simultaneously both highly spectrally efficient and power efficient.